In general, a text particularly on an electronic display can be very hard to be read (deeply fathomed) by a reader due to the difficulty of holding view point optimally (with spatiotemporal optimality (precision)) at where to be gazed at by the reader, and the best possible information absorption from an electronically displayed text is frequently unattained.
Without achieving adequate absorption of information, the reader would gradually lose the willingness to read the electronically displayed texts.
It is currently very difficult to underline (highlight) the segments of an electronically displayed text (electronic document) a reader wants underlined (highlighted) at will with rapidity, compared to manually underlining (highlighting) a printed text.
This could result in a reader's forgetting most of what has once been understood from laborious, time-consuming reading of an electronically displayed text, because afterwards it can become very hard for the reader to reread that text selectively and efficiently with laying emphasis on the segments especially important for the reader.
A reader's manually underlining (highlighting) several segments in a (printed) text could interfere with continuousness of reading when a segment to be underlined (highlighted) is retroactively determined after adjacent, prior several lines (or segments) have been read by the reader.
Although establishing what comprehended from reading as practical knowledge necessitates rereading (review), effective rereading (review) is extremely difficult to be practiced without the present invention.